It is useful for a photographer to know the distances from a camera to various locations in a scene to be photographed. For example, a photographer may wish to choose an aperture setting and focus distance so that certain objects in the scene are sharply focused in the resulting photograph. Or a photographer may wish to choose an amount of supplemental flash illumination such that distant objects receive an effective amount of supplemental light while near objects are not illuminated too brightly.
Distance information is useful for post-processing of a photograph as well.
For example, objects in a photograph taken with flash may be digitally brightened or darkened based on their distance from the camera so that the scene appears evenly illuminated.
An automatic camera may exploit distance information in similar ways, choosing photographic settings automatically based on known distances.
Typically, a camera focuses on only a small region or single subject in a scene. The distance from the camera to the subject of focus can be derived from the positions of elements in the camera lens, but this method gives no information about distances to other objects in the scene. Some cameras provide a “depth of field mode”, wherein the photographer can direct the camera to focus on multiple scene locations one at a time, and the camera uses the multiple focus measurements to select settings for taking a photograph. This technique adds to the time required to take a photograph.
Other methods of measuring distances to multiple scene locations may add cost and complexity to a camera.